:PROPERTIES:
:ID:       434ee61c-4461-424f-8dba-5c86ddb06c3c
:END:
#+title: Monoid

A [[id:b22a1c70-02a7-49ce-b5e7-407f1064cd0c][Semigroup]] with an identity value.

In [[id:9ac78677-2602-4a06-af0a-4ed82e98a9b6][Haskell]], the function representing the identity value for a given Monoid is
=mempty=.

#+caption: =mempty= in Haskell
#+begin_src haskell :exports code
  mempty :: Monoid a => a
#+end_src

* Examples
**  List
Combined with =append=, identity value is the empty list (=[]=)
**  Number Addition
Combined with =+=, identity value is =0=
**  Number Multiplication
Combined with =*=, identity value is =1=